Tag Archives: David Labonte

A team of zoology researchers at Cambridge University (UK) find themselves in the unenviable position of having their peer-reviewed study used as a source of unintentional humour. I gather zoologists (Cambridge) and engineers (Stanford) don’t have much opportunity to share information.

Latest research reveals why geckos are the largest animals able to scale smooth vertical walls — even larger climbers would require unmanageably large sticky footpads. Scientists estimate that a human would need adhesive pads covering 40% of their body surface in order to walk up a wall like Spiderman, and believe their insights have implications for the feasibility of large-scale, gecko-like adhesives.

Dr David Labonte and his colleagues in the University of Cambridge’s Department of Zoology found that tiny mites use approximately 200 times less of their total body area for adhesive pads than geckos, nature’s largest adhesion-based climbers. And humans? We’d need about 40% of our total body surface, or roughly 80% of our front, to be covered in sticky footpads if we wanted to do a convincing Spiderman impression.

Once an animal is big enough to need a substantial fraction of its body surface to be covered in sticky footpads, the necessary morphological changes would make the evolution of this trait impractical, suggests Labonte.

“If a human, for example, wanted to walk up a wall the way a gecko does, we’d need impractically large sticky feet – our shoes would need to be a European size 145 or a US size 114,” says Walter Federle, senior author also from Cambridge’s Department of Zoology.

The researchers say that these insights into the size limits of sticky footpads could have profound implications for developing large-scale bio-inspired adhesives, which are currently only effective on very small areas.

“As animals increase in size, the amount of body surface area per volume decreases – an ant has a lot of surface area and very little volume, and a blue whale is mostly volume with not much surface area” explains Labonte.

“This poses a problem for larger climbing species because, when they are bigger and heavier, they need more sticking power to be able to adhere to vertical or inverted surfaces, but they have comparatively less body surface available to cover with sticky footpads. This implies that there is a size limit to sticky footpads as an evolutionary solution to climbing – and that turns out to be about the size of a gecko.”

Larger animals have evolved alternative strategies to help them climb, such as claws and toes to grip with.

The researchers compared the weight and footpad size of 225 climbing animal species including insects, frogs, spiders, lizards and even a mammal.

“We compared animals covering more than seven orders of magnitude in weight, which is roughly the same as comparing a cockroach to the weight of Big Ben, for example,” says Labonte.

These investigations also gave the researchers greater insights into how the size of adhesive footpads is influenced and constrained by the animals’ evolutionary history.

“We were looking at vastly different animals – a spider and a gecko are about as different as a human is to an ant- but if you look at their feet, they have remarkably similar footpads,” says Labonte.

“Adhesive pads of climbing animals are a prime example of convergent evolution – where multiple species have independently, through very different evolutionary histories, arrived at the same solution to a problem. When this happens, it’s a clear sign that it must be a very good solution.”

The researchers believe we can learn from these evolutionary solutions in the development of large-scale manmade adhesives.

“Our study emphasises the importance of scaling for animal adhesion, and scaling is also essential for improving the performance of adhesives over much larger areas. There is a lot of interesting work still to do looking into the strategies that animals have developed in order to maintain the ability to scale smooth walls, which would likely also have very useful applications in the development of large-scale, powerful yet controllable adhesives,” says Labonte.

There is one other possible solution to the problem of how to stick when you’re a large animal, and that’s to make your sticky footpads even stickier.

“We noticed that within closely related species pad size was not increasing fast enough to match body size, probably a result of evolutionary constraints. Yet these animals can still stick to walls,” says Christofer Clemente, a co-author from the University of the Sunshine Coast [Australia].

“Within frogs, we found that they have switched to this second option of making pads stickier rather than bigger. It’s remarkable that we see two different evolutionary solutions to the problem of getting big and sticking to walls,” says Clemente.

“Across all species the problem is solved by evolving relatively bigger pads, but this does not seem possible within closely related species, probably since there is not enough morphological diversity to allow it. Instead, within these closely related groups, pads get stickier. This is a great example of evolutionary constraint and innovation.”

A researcher at Stanford University (US) took strong exception to the Cambridge team’s conclusions , from a Jan. 28, 2016 article by Michael Grothaus for Fast Company (Note: A link has been removed),

It seems the dreams of the web-slinger’s fans were crushed forever—that is until a rival university swooped in and saved the day. A team of engineers working with mechanical engineering graduate student Elliot Hawkes at Stanford University have announced [in 2014] that they’ve invented a device called “gecko gloves” that proves the Cambridge researchers wrong.

Hawkes has created a video outlining the nature of his dispute with Cambridge University and US tv talk show host, Stephen Colbert who featured the Cambridge University research in one of his monologues,

Each handheld gecko pad is covered with 24 adhesive tiles, and each of these is covered with sawtooth-shape polymer structures each 100 micrometers long (about the width of a human hair).

The pads are connected to special degressive springs, which become less stiff the further they are stretched. This characteristic means that when the springs are pulled upon, they apply an identical force to each adhesive tile and cause the sawtooth-like structures to flatten.

“When the pad first touches the surface, only the tips touch, so it’s not sticky,” said co-author Eric Eason, a graduate student in applied physics. “But when the load is applied, and the wedges turn over and come into contact with the surface, that creates the adhesion force.”

As with actual geckos, the adhesives can be “turned” on and off. Simply release the load tension, and the pad loses its stickiness. “It can attach and detach with very little wasted energy,” Eason said.

The ability of the device to scale up controllable adhesion to support large loads makes it attractive for several applications beyond human climbing, said Mark Cutkosky, the Fletcher Jones Chair in the School of Engineering and senior author on the paper.

“Some of the applications we’re thinking of involve manufacturing robots that lift large glass panels or liquid-crystal displays,” Cutkosky said. “We’re also working on a project with NASA’s Jet Propulsion Laboratory to apply these to the robotic arms of spacecraft that could gently latch on to orbital space debris, such as fuel tanks and solar panels, and move it to an orbital graveyard or pitch it toward Earth to burn up.”

Previous work on synthetic and gecko adhesives showed that adhesive strength decreased as the size increased. In contrast, the engineers have shown that the special springs in their device make it possible to maintain the same adhesive strength at all sizes from a square millimeter to the size of a human hand.

The current version of the device can support about 200 pounds, Hawkes said, but, theoretically, increasing its size by 10 times would allow it to carry almost 2,000 pounds.

To be fair to the Cambridge researchers, It’s stretching it a bit to say that Hawke’s gecko gloves allow someone to be like Spiderman. That’s a very careful, slow climb achieved in a relatively short period of time. Can the human body remain suspended that way for more than a few minutes? How big do your sticky pads have to be if you’re going to have the same wall-climbing ease of movement and staying power of either a gecko or Spiderman?

The University of Cambridge (UK) has produced research that could lead to cleaning at the microscale and nanoscale and it’s all due to ants. From a July 28, 2015 news item on Nanowerk (Note: A link has been removed),

For an insect, grooming is a serious business. If the incredibly sensitive hairs on their antennae get too dirty, they are unable to smell food, follow pheromone trails or communicate. So insects spend a significant proportion of their time just keeping themselves clean. Until now, however, no-one has really investigated the mechanics of how they actually go about this.

In a study published in Open Science (“Functional morphology and efficiency of the antenna cleaner in Camponotus rufifemur ants”), Alexander Hackmann and colleagues from the Department of Zoology [University of Cambridge] have undertaken the first biomechanical investigation of how ants use different types of hairs in their cleaning apparatus to clear away dirt from their antennae.

“Insects have developed ingenious ways of cleaning very small, sensitive structures, so finding out exactly how they work could have fascinating applications for nanotechnology – where contamination of small things, especially electronic devices, is a big problem. Different insects have all kinds of different cleaning devices, but no-one has really looked at their mechanical function in detail before,” explains Hackmann.

Camponotus rufifemur ants possess a specialised cleaning structure on their front legs that is actively used to groom their antennae. A notch and spur covered in different types of hairs form a cleaning device similar in shape to a tiny lobster claw. During a cleaning movement, the antenna is pulled through the device which clears away dirt particles using ‘bristles’, a ‘comb’ and a ‘brush’.

To investigate how the different hairs work, Hackmann painstakingly constructed an experimental mechanism to mimic the ant’s movements and pull antennae through the cleaning structure under a powerful microscope. This allowed him to film the process in extreme close up and to measure the cleaning efficiency of the hairs using fluorescent particles.

What he discovered was that the three clusters of hairs perform a different function in the cleaning process. The dirty antenna surface first comes into contact with the ‘bristles’ (shown in the image in red) which scratch away the largest particles. It is then drawn past the ‘comb’ (shown in the image in blue) which removes smaller particles that get trapped between the comb hairs. Finally, it is drawn through the ‘brush’ (shown in the image in green) which removes the smallest particles.

Scanning electron micrograph of the tarsal notch (Alexander Hackmann). Courtesy: University of Cambridge

The news release offers more detail about the ‘notch’s’ cleaning properties,

“While the ‘bristles’ and the ‘comb’ scrape off larger particles mechanically, the ‘brush’ seems to attract smaller dirt particles from the antenna by adhesion,” says Hackmann, who works in the laboratory of Dr Walter Federle.

Where the ‘bristles’ and ‘comb’ are rounded and fairly rigid, the ‘brush’ hairs are flat, bendy and covered in ridges – this increases the surface area for contact with the dirt particles, which stick to the hairs. Researchers do not yet know what makes the ‘brush’ hairs sticky – whether it is due to electrostatic forces, sticky secretions, or a combination of factors.

“The arrangement of ‘bristles’, ‘combs’ and ‘brush’ lets the cleaning structure work as a particle filter that can clean different sized dirt particles with a single cleaning stroke,” says Hackmann. “Modern nanofabrication techniques face similar problems with surface contamination, and as a result the fabrication of micron-scale devices requires very expensive cleanroom technology. We hope that understanding the biological system will lead to building bioinspired devices for cleaning on micro and nano scales.”